Your Resource for all Things Relating to Factor V Leiden

How Serious is Factor V Leiden?

Venous thromboembolism (VTE) is a major medical problem, which affects approximately 1 in 1,000 persons per year. VTE is a multicausal disease that results from multiple interactions between genetic, acquired, and circumstantial risk factors.


Factor V Leiden is the most common genetic risk factor for VTE and is found in up to 50% of patients with VTE and 50% of patients with familial thrombophilia. It is found in 50% to 70% of all recurrent VTE patients.


Factor V Leiden can be serious in that it does not display any symptoms that you would be able to detect to suggest that you have the disorder prior to the development of a blood clot or complications with a pregnancy.


Researchers have identified some known “triggers” that, when combined with Factor V Leiden, greatly increase the risks of developing a blood clot. However, there is still a lot that is not known about Factor V Leiden.


Testing for Factor V Leiden in asymptomatic individuals is a very controversial issue in the medical and genetic communities with all offering many different viewpoints. While the debate goes on, it is safe to assume that there are people at risk because they are unaware they carry the genetic disorder. Not only are they unaware that they carry Factor V Leiden, but their direct family members such as their parents, children, brothers and sisters who may carry the mutated gene are also at risk.


The best treatment for Factor V Leiden carriers who have not had venous blood clots but have other risk factors is unclear. The medical community is working to find that balance between the risks and benefits of treating versus not treating those individuals. There is still a lot that is unknown about the best treatment of Factor V Leiden.


Current estimates show that 90% to 95% of people with Factor V Leiden will not develop blood clots during their lifetime. In the 5% to 10% of people who do, these abnormal blood clots can lead to long-term health problems or become life threatening if they break loose and travel to the lungs.


Many people who feel they are perfectly healthy one day are suddenly finding themselves dealing with the sometimes life changing effects of a genetic blood clotting disorder they have never heard of… we hope to change that.

Can I pass Factor V Leiden on to my children?

Yes, depending on how many copies of the mutated gene you have and your spouse has, there is a relatively good chance that you will pass the genetic disorder on to your children.

  • We all inherit two copies of the factor V gene. We inherit one copy from our mother and the other from our father. As a result, our risk for having Factor V Leiden thrombophilia depends on the genetic status of each of our parents.
  • Most people with Factor V Leiden thrombophilia have one “normal” factor V gene and one with the Factor V Leiden gene mutation. People with one copy of the mutation are called “heterozygotes”.
  • If you have the heterozygous type of Factor V Leiden and your spouse has the normal factor V gene, there is a 50% chance that your child will inherit a Factor V Leiden gene from you. There is also a 50% chance that your child will inherit your normal Factor V gene and not have Factor V Leiden.
  • Factor V Leiden thrombophilia is a relatively common condition. In some families, both parents have one Factor V Leiden gene and one normal factor V gene. In this scenario, each child of the couple would have a 25% chance of having two mutations, a 25% chance of having no mutation, and a 50% chance of having one mutation.
  • People with two copies of the factor V mutation are said to be “homozygotes.”
  • If you have the more dangerous homozygous type of Factor V Leiden, there is a 100% chance you will pass Factor V Leiden on to your children. Your child will either have the heterozygous or homozygous type, depending on whether the gene passed down from his or her other parent is normal (Factor V) or abnormal (Factor V Leiden).

Why is Factor V Leiden dangerous? (and what action steps can I take to reduce the risks)

Not everyone who develops a venous blood clot has Factor V Leiden. Of those who do, an estimated 40-60% carry the Factor V Leiden genetic mutation depending on age and other contributing factors.


Venous blood clots do not discriminate. Science has made major strides in recent years in understanding the very complex blood clotting process known as the clotting cascade. However, although we understand to a large extent the mechanics or the “how” portion of the process, we are still not able to fully understand “why that particular person developed a blood clot” or accurately predict the 10% of the Factor V Leiden population “who will develop a blood clot.”


Venous thromboembolism is a multi-causal disease meaning that venous blood clots can sometimes develop as a result of two or more genetic, acquired, circumstantial, social, or physiological factors or “triggers” coming together in a person who appears to be perfectly healthy. It is these sometimes unknown “triggers” combined with Factor V Leiden that makes Factor V Leiden dangerous.

Factor V Leiden is dangerous because there are no early symptoms or warning signs. Factor V Leiden does not display any symptoms that you would be able to detect to suggest that you have the disorder.

Take Action - Get Tested

If blood clots have occurred in your family and you suspect you may have or just want to know if you have the disorder, talk to your medical professional about getting tested.

A recent study showed that 81% of people who found out they have Factor V Leiden felt they benefited in becoming aware, 83% felt they now had an increased risk perception of developing a blood clot, 84% shared the test results with family and/or their health care providers and 57% took action to reduce their risk after finding out.


If you or any of your family members have had issues with blood clots, ask your doctor to perform the simple blood test to see if you have it.


If you find out you do carry the Factor V Leiden gene mutation, make your parents, brothers, sisters, and children aware of your diagnosis so they too are mindful that they could potentially have the disorder as well.


If you don't know you have Factor V Leiden, you could unknowingly do those things that, combined with Factor V Leiden, are known to greatly increase your risks of “triggering” a venous blood clot.

Take Action - Get Help and Counseling from Your Medical Professional

Get help and counseling from your medical professional concerning the dangers and circumstances about when blood clots can occur and what steps you can take to reduce the risks.


Something as simple as getting up and walking around on a long flight could save your life.


Venous blood clots can kill or cause health-related issues that can last for the rest of your life.

Venous blood clots can kill or cause health-related issues that can last for the rest of your life.

Take Action - Tell Your Doctor

If you know you have Factor V Leiden, be sure to make your medical professional aware.

He or she can make any necessary changes to your plan of care and make a better diagnosis should you begin showing symptoms of a venous blood clot.

You can pass the genetic disorder on to your children and expose them to the same risks of venous blood clots.

Take Action - Tell Your Family

If you know you carry Factor V Leiden, make your direct family aware such as your parents, brothers, sisters, and children.


They can then work with their medical professional about the need to get tested and, if necessary, make any life style changes or take simple steps to reduce their risks throughout their lifetime.

The American Factor V Leiden Association is working hard to promote public awareness, provide education, and be a resource for knowledge.

Our current program initiative on testing is aimed at improving testing guidelines by taking a common sense approach and looking at all variables related to the disorder.

The American Factor V Leiden Association hopes to publish an in-depth position statement on Factor V Leiden testing in the coming months.

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